At the title screen, press Left, Right, Up, Down. Then, hold Z and press Right(2), Left(2). If you entered the code correctly, you will hear a sound. Then while playing the game, press A + B + R for full health, full ammunition, and all weapons.

Level select

At the title screen, hold Z and press Right, Down(2), Right. Release Z, then press Right, Up, Down, Left(2), Up, Right(2). If you entered the code correctly, you will hear a sound.

Invincibility

At the title screen, hold Z and press R(2), L(2), Up, Down, Left, Right. If you entered the code correctly, you will hear a sound.

Play as Dark Stinger

Before the opening screen appears, hold Z + Analog-stick Up and press C-Up, C-Right, C-Down, C-Left(5), B, A, B. If you entered the code correctly, you will hear a sound.